What Is ETF Tracking Error and How to Minimize It
Your ETF does not perfectly match its index. Here is why, how much it matters, and when tracking error is a red flag.
Don't have time? Here's what you need to know:
- 1Tracking error measures how closely an ETF follows its index — lower is better
- 2For U.S. stock ETFs, annual tracking difference should be within 0.05% of the expense ratio
- 3International ETFs have higher tracking error (0.10-0.30%) due to withholding taxes
- 4Commodity ETFs have the worst tracking (0.50-2.00%) due to futures rolling costs
Tracking Error: The Gap Between Your ETF and Its Index
Tracking error measures how closely an ETF's returns follow its benchmark index. If the S&P 500 returns 10.00% and VOO returns 9.97%, the tracking difference is 0.03% — essentially the expense ratio. Tracking error (the standard deviation of daily return differences) tells you how consistently the fund matches the index day-to-day.
For major index ETFs, tracking error is negligible. VOO and VTI track their indices within 0.01-0.05% per year. Problems arise with international ETFs (withholding taxes and time zone differences create gaps), synthetic ETFs (counterparty risk adds variability), and commodity ETFs (futures rolling creates persistent drag).
What Causes Tracking Error
| Cause | How It Creates Error | Which ETFs Are Affected |
|---|---|---|
| Expense ratio | Fund returns = index minus fee | All ETFs (0.03-1.00%) |
| Cash drag | Fund holds small cash buffers for redemptions | All ETFs (minimal for large funds) |
| Withholding taxes | Foreign governments tax dividends before fund receives them | International ETFs (VXUS, VWO) |
| Sampling | Fund holds a subset of the index rather than all stocks | Large-index ETFs with 3,000+ stocks |
| Futures rolling | Commodity futures contracts must be periodically replaced | Commodity ETFs (DBC, USO) |
| Rebalancing timing | Fund rebalances on different dates than the index | Factor and smart beta ETFs |
How Much Is Acceptable
For a U.S. stock index ETF: annual tracking difference should be within 0.05% of the expense ratio. If VOO charges 0.03%, its annual underperformance vs the S&P 500 should be about 0.03%. If it underperforms by 0.20%, something is wrong. For international ETFs: up to 0.30% is common due to withholding taxes. For commodity ETFs: 0.50-2.00% annual drag from futures rolling is normal (and a reason to be cautious with these products).
Check the fund's annual report or fact sheet for 'tracking difference' — the actual annual return gap vs the index. This single number tells you more than the marketed expense ratio.
Tip: Some ETFs actually outperform their index (negative tracking difference) due to securities lending revenue offsetting the expense ratio. This is common with Vanguard and iShares funds.
Ready to invest? Open an IBKR account in 10 minutes and get free stock. $0 commissions on US ETFs • Fractional shares from $1 • 150+ global markets.
Frequently Asked Questions
Is tracking error the same as tracking difference?
No. Tracking error is the volatility (standard deviation) of daily return differences — it measures consistency. Tracking difference is the actual annual return gap — it measures how much you underperformed (or outperformed) the index. Tracking difference is more useful for investors.
Should I worry about tracking error on VTI?
No. VTI's tracking difference is typically 0.00-0.03% per year — essentially the expense ratio. For a well-managed broad U.S. index ETF, tracking error is a non-issue.
Why do commodity ETFs have such high tracking error?
They use futures contracts that must be 'rolled' (sold and replaced) regularly. When future contracts cost more than the spot price (contango), each roll loses money. This creates a persistent drag that can exceed 2% per year for some commodity ETFs.
Further Reading
Free Tools
Alex Harrington
CFA Level II Candidate, Finance & Economics
Alex Harrington is an independent ETF researcher and personal finance writer with over 8 years of experience analyzing exchange-traded funds. A CFA Level II candidate with a background in economics, Alex has reviewed 800+ ETFs and helped thousands of beginners build their first investment portfolios through clear, jargon-free education.
This content is for educational purposes only and does not constitute financial advice. Past performance does not guarantee future results. Consult a licensed financial advisor before making investment decisions.